1. Field of the Invention
The present invention relates to an image sensor and a method for manufacturing the same, and more particularly to a back side illumination image sensor reduced in chip size, which has a capacitor disposed in a vertical upper portion of a pixel region in the back side illumination image sensor where light is illuminated from a back side of a subscriber, thereby reducing a chip size, and a method for manufacturing the back side illumination image sensor.
2. Description of the Related Art
In general, an image sensor is a semiconductor device which converts optical image signals into electrical signals. A CCD includes respective metal-oxide semiconductor (MOS) capacitors that are very close to each other for storing and transferring electric charge carriers. A CMOS image sensor has adapted a switching scheme of making MOS transistors as many as pixels with a CMOS technology, which uses a control circuit and a signal-processing circuit as peripheral circuits, and of detecting outputs in turn with the MOS transistors.
FIG. 1 is a view schematically illustrating the configuration of a conventional CMOS image sensor, and FIG. 2 is a cross-sectional view schematically illustrating the configuration of the conventional CMOS image sensor.
As shown in FIGS. 1 and 2, the conventional CMOS image sensor 100 includes a pixel region 120, a peripheral circuit region 130, and a capacitor region 140. The pixel region 120 contains photodiodes for receiving light and generating photocharge, and transfer transistors for transferring photocharge to sensing nodes of pixels. The peripheral circuit region 130 converts sensed light into data via electrical signals.
In the pixel region 120, pixels having photodiodes PD are formed beneath the surface of a semiconductor substrate 110; and a multi-layered insulating layer and a multi-layered metal wiring layer M1 and M2, together with transfer transistors Tx, are formed on top of the semiconductor substrate 110; and light is illuminated from the front side of the semiconductor substrate 110 (Front Side Illumination).
That is, since the conventional front side illumination image sensor collects optical signals from the front side of a substrate (i.e. from the top of photodiodes), it is impossible to form metal wiring layers, which may obstruct the incidence of light, in the vertical popper portion of the photodiodes. Therefore, except for a metal wiring layer formed within a region which does not obstructs light incident to the photodiodes, the other metal wirings and capacitors are formed in the outside of the pixel region.
As described above, the conventional CMOS image sensor requires a separate area for forming capacitors in the outside of the pixel region, thereby increasing the size of a unit pixel, so that it is difficult to reduce the chip size.